Re: [Xen-devel] [PATCH V2] tools/xenstore-watch: Add new timeout parameter

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Razvan Cojocaru writes ("[PATCH V2] tools/xenstore-watch: Add new timeout 
parameter"):
> This patch allows xenstore-watch to exit even if no changes to its
> XenStore key have occured in a specified interval (in seconds), via
> a new -T parameter.

I realise I come a bit late with this, but:

I'm not opposed to making it possible to wait with a timeout for a
suitable situation in xenstore.

However, xenstore-watch needs to be run in a loop because of the
possibility of spurious watch triggers.  And this means that to use
your new option and get the timeout right, the caller would need to
write shell code to query the time, do arithmetic to calculate the
appropriate timeout, and so on.

Or to put it another way, xenstore-watch is a fine debugging and
monitoring tool but not very good for scripting.

For scripting what you probably want is something like:

  "wait up to T seconds for xenstore node /X/Y/Z
   to contain something matching PAT; bail immediately if
   /X/Y/Z contains something matching QAT".

How are you using this new option ?

Ian.

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